1. Field of the Invention
The present invention relates to a battery separator.
2. Description of the Related Art
In a battery, a separator is used to separate a positive electrode and a negative electrode from each other to prevent a short circuit therebetween, and further, to hold an electrolyte thereon and enable a smoothelectromotive reaction.
Recently, in electronic equipment, a space allotted for the battery has become smaller due to the need for miniaturization and weight-saving. Nevertheless, the performance requirement for such a smaller battery is the same as or higher than that for a conventional battery, and therefore, it is necessary to enhance the capacity of the battery, and to increase the amounts of active materials in the electrodes. Accordingly, a volume allotted in the battery for the separator must be reduced. Although a thin separator having a thickness of 0.15 mm was proposed, a thinner separator having a thickness of 0.1 mm or less is desired in the market.
A separator that can be thinned to a thickness of 0.1 mm or less is proposed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 11-126595. This Publication discloses an alkaline battery separator having a mass per unit area of 15 to 55 g/m2, a void rate of 40 to 80%, and a thickness of 0.05 to 0.12 mm, and composed of a laminated nonwoven fabric prepared by adhering fine-fiber nonwoven fabrics onto both sides of a nonwoven fabric produced by a wet-laid method and containing sheath-core type composite fibers consisting of a sheath polymer with a low melting point and a core polymer with a high melting point.
However, the separator disclosed in the above Japanese Unexamined Patent Publication (Kokai) No. 11-126595 is composed of the laminated nonwoven fabric prepared by adhering fine-fiber nonwoven fabrics and the nonwoven fabric produced by a wet-laid method, and thus, the electrolyte is unevenly distributed at the fine-fiber nonwoven fabrics. Therefore, an inner pressure is increased, and as a result, it becomes difficult to enhance the capacity of the battery, although the separator is designed to be thinner to enable an enhancement of the capacity of the battery.